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1988 GMC PU 5.7 V8, Mysterious engine troubles
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georgejg
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Jun 10, 2014, 6:40 AM
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1988 GMC PU 5.7 V8, Mysterious engine troubles
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1988 GMC 1 Ton PU
5.7 V8
110,000 miles
I came home from a trip, truck ran fine, no problem at all; shut it off.
Next morning, went to start truck, hard to start, when it does start, only runs 5-7 seconds very poorly.
Compression check: 4 cylinders are 30 lbs compression.
Removed dome, 5 bent push rods.
Removed timing chain cover, timing is right on marks, chain has 3/8" play.
It's not the timing, and I don't know what the problem is.
Please help!
Thanks to all.
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Discretesignals
Ultimate Carjunky
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Jun 10, 2014, 6:56 AM
Post #2 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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Any modifications done on this engine?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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kev2
Veteran
Jun 10, 2014, 8:29 AM
Post #3 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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something not right in post description-
ran good then parked.
next morning no start- 5 bent pushrods?
30lbs compression?
what cylinders had 30lbs and what cylinder had bent pushrods?
all on same bank?
Look in oil pan for evidence of coolant or fuel .....advise.
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georgejg
New User
Jun 12, 2014, 2:12 AM
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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No. Stock engine
On the two banks, the two front cylinders and two back cylinders had 30 lbs compression, and had bent push rods.
Second cylinder on driver's side bank also had bent push rod.
Compression for rest of cylinders was 100 plus lbs.
No fuel or water in oil.
(This post was edited by georgejg on Jun 12, 2014, 2:18 AM)
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Discretesignals
Ultimate Carjunky
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Jun 12, 2014, 2:28 AM
Post #5 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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This is a strange one. Did you remove the chain sprockets and inspect the dowel pin on the cam and the woodruff key on the crank to see if they had sheared?
edit: forgot the cam spocket is held on by 3 bolts, so it would be unlikely that would shear, but the crank sprocket is a possibility.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jun 12, 2014, 2:37 AM)
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kev2
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Jun 12, 2014, 2:52 AM
Post #6 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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interesting ran smooth - parked (no one drove it) and then BAM this issue...
My thinking on fuel and coolant was hydrostatic lock... that isn't it - colleague is thinking a timing chain drive issue- easy check
try this remove dist cap make note of rotor position then crank engine is rotor moving?
how damaged are the pushrods- catastrophic or just bowed?
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Discretesignals
Ultimate Carjunky
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Jun 12, 2014, 2:56 AM
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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Don't think a hydrostatic lock would cause bent pushrods because a hydro-lock condition would have to occur when the valves are closed? The only thing I could think that would cause bent pushrods is if the valves in those cylinder where open as the piston was TDC. The only things that I can think of that would cause something like that would be valve train issues such as valve springs binding, high lift camshaft, broken camshaft, incorrect valve timing, etc.
I definitely agree with you Kev that it is very strange that the problem all the sudden occurring as it did.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jun 12, 2014, 3:04 AM)
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Hammer Time
Ultimate Carjunky
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Jun 12, 2014, 3:23 AM
Post #8 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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Are we sure there are no teenagers in this picture?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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kev2
Veteran
Jun 12, 2014, 9:06 AM
Post #9 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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we are trying to figure out the unexplainable would have, could have, may have - I think Hammer has the best scenario.
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georgejg
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Jun 16, 2014, 3:07 AM
Post #10 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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3 push rods are catastrophically bent, 2 are broken into two pieces each.
There is absolutely no possibility of anyone driving it. No teenagers in the picture, no wife, and the dog never learned how to drive. I live in a rural area, so no neighbors either.
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Tom Greenleaf
Ultimate Carjunky
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Jun 16, 2014, 3:15 AM
Post #11 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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It's "Mysterious" alight!
Not sure but if you have the push rods all out MAYBE just try new ones (cheap) to see if it does it again right away? AYOR - this doesn't add up at all and worry about this engine.
Super rare under the conditions, age, miles that something wild like camshaft broke (they can but usually provoked or right away new) and weak links beyond that just took the hit?
If they didn't break from replacing them it could make diagnosis easier or even possible without a million hours of figuring out how that was possible as described...........
Tom
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Hammer Time
Ultimate Carjunky
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Jun 16, 2014, 3:39 AM
Post #12 of 13
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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I would probably replace the push rods and rotate the engine by hand with the valve covers off to see if everything is moving.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Jun 16, 2014, 3:56 AM
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Re: 1988 GMC PU 5.7 V8, Mysterious engine troubles
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Yes - The one known of I didn't see (was tech teacher's Father's car) but was exposed to wild revving when cold (he was deaf) and cam split in such a way that it still turned but all off of course. That one at least had a reason. So far to me this one lasted this long so sudden issues of the sort with not telling us of provocation is wildly rare to me.
Even if uncared for and sludged up bad, no oil or no oil pressure I doubt it would fail in this way????????????
T
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